Does being cold help us lose weight?

Could the secret to January weight loss be as simple as turning down the heating? It's a strange-sounding question, but actually not as leftfield as you might think. In recent years, researchers have been investigating a particular type of fat – brown fat – which burns around five times as many calories as 'normal' fat. This kind of fat is activated when you spend time in the cold.

As Professor Barbara Cannon, a physiologist at the Wenner-Gren Institute in Stockholm explains, brown fat acts very differently from the variety we may be trying to lose:

"Our normal fat tissue, the white variety, is mainly a storage place for energy in the form of fat. Brown fat cells, on the other hand, are filled with mitochondria where fat combustion takes place. The cells first burn the fat they contain, but then import fat from the white fat stores and in this way reduce the stores."

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She adds that cold exposure revs up the production of brown fat cells:

"When we feel cold, the nervous system sends signals to the temperature sensing region of the brain, which then activates the nerves that travel to brown fat. These stimulate increased cell proliferation and cell development."

In theory, then, forgoing that extra jumper might crank your fat burning potential up a notch. So what does that mean for those of us with some festive jiggle to lose?

Many adults have brown fat

The study of brown fat is relatively new. We have known for a long time that newborn babies (who can't shiver) use deposits of brown fat to keep them warm. However, it wasn't until the late 2000s that researchers discovered that most – if not all – adults have a small amount of brown fat too.

Cannon recalls: "Suddenly it was accepted that brown fat was found in adults and could theoretically be used for slimming. Lots and lots of articles have followed."

It can be hard to pinpoint the location of these cells, but scans suggest they are found in surprising places – most typically around the neck and shoulders, in the chest or even down the spine.

Brown fat could have multiple health benefits

In one 2012 study, volunteers wore a cold suit for three hours, which decreased their body temperature without making them shiver. They burned an extra 250 calories over that period.

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The exact figure will depend on the person. Another study found that, when subjects sat in a 15oC room for two hours wearing summer clothing, their brown fat burned between 100 and 250 calories each time. The variance may depend on factors like age and gender, and some studies suggest brown fat activity increases with repeated exposure to cold.

Calorie burning, however, is only part of it. Brown fat is thought to play a direct role in stabilising blood sugar, which means it may help fight diabetes. One study found that mice given brown fat transplants processed glucose better and had reduced insulin resistance.

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Brown fat has also been shown to lower cholesterol and triglyceride levels, which means there are implications for heart health too.

The overall effect may be quite small

Barbara Cannon says we need to be realistic about the possibilities. She believes that, while brown fat could be harnessed to increase energy expenditure to some extent, it is unlikely to be the be-all and end-all of weight loss. As she explains:

"We know that different people have different amounts of brown fat for various reasons (genetic, environmental) and those with more have been shown to be somewhat slimmer. There are results – though not very strong ones – indicating that people can get more brown fat again if cold-exposed."

However, she points out that we always increase our metabolism in the cold anyway, whether or not brown fat is playing a role. She says:

"If we don't have brown fat then we have to shiver – which is of course uncomfortable and unpleasant. One conclusion, then, is that we always expend more energy in the cold and thus could theoretically become slim by this – but it is only if we have brown fat that it is comfortable and we don't think about it. All of this assumes that we don't eat more to compensate what we have burnt."

There may one day be a pill to activate brown fat

While this research is still in its early stages, we may one day see a wave of interventions that harness the benefits of brown fat.

But for the time being, it is best to stick with all the advice we already know about staying healthy – minimising stress, eating a healthy diet, sleeping well and taking regular exercise.

As for turning down the thermostat a couple of degrees? While it is not possible to say this will definitely have an effect (and we definitely wouldn't recommend exposing yourself to cold temperatures on purpose), if you can tolerate a slight chill it can't hurt!

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